A refrigerator cabinet has its outer case fabricated from a sheet of metal. Prior to folding a sheet of metal, it is necessary to apply a liquid mold release chemical to selected areas of the outer case.
The liquid mold release chemical is utilized as a lubricant to enable a plastic liner, which is mounted in a groove formed in the outer case adjacent its front flange that is formed by one of the side flanges of the sheet of metal, to have movement relative to the outer case during spraying of foam insulation. This is because the outer case expands when foam insulation is sprayed at a relatively high temperature in a liquid state and the outer case contracts during curing of the foam insulation to its solid state. This contraction and expansion of the outer case could possibly cause the plastic liner to crack if it could not move relative to the outer case. Accordingly, the use of the liquid mold release chemical prevents this potential damage to the plastic liner.
It also is necessary to prevent the application of this material to areas where the sheet of metal is folded and at the leading and trailing edges of the sheet of metal. The sheet of metal has notches formed in each of its side flanges at each of the locations at which the sheet of metal is to be folded to form the outer case. Thus, each of the fold areas is identified by the presence of the notch.
It is desired to prevent any of the liquid mold release chemical from entering the groove in one of the side flanges of the sheet of metal at each of the notches. This is because a corner bracket is installed at each of the notches where folding of the sheet of metal occurs to form the outer case, and the liquid mold release chemical would be picked up by the equipment to cause the equipment to eventually become dirty whereby it might cease to function.
U.S. Pat. No. 4,389,971 to Schmidt discloses the application of glue to a single area beginning a predetermined distance from the leading edge of a paper board box blank and stopping a predetermined distance from the trailing edge of the box blank. Since the aforesaid Schmidt patent seeks to have all the area therebetween covered with glue, there is no recognition of any interruption of this single defined glue area.
U.S. Pat. No. 3,245,376 to Romstadt activates spray guns when a leading edge of a glass sheet interrupts a light beam and deactivates them when a trailing edge moves past the beam. The aforesaid Romstadt patent also has additional spray guns to provide thickened portions in the corners of the glass sheet.
U.S. Pat. No. 3,607,340 to Stroupe applies a spot coating or a continuous coating to a sheet of material. The aforesaid Stroupe patent has sensing means, which is responsive to the presence of a sheet or indicia thereon, for generating a signal to a delay device that controls the length of time the coating is applied. There is no recognition in the aforesaid Stroupe patent of starting and stopping the application of material to a moving part in accordance with when portions of the moving part arrive at certain positions relative to the material application means.
U.S. Pat. No. 3,646,521 to Porter sprays objects of diverse geometry. While a lead-lag control circuit is utilized in the aforesaid Porter patent to not coat a portion of an object, there is no recognition of sensing the presence of certain portions of the object for utilization in determining when there is to be no spraying of material on the object.
The method and apparatus of the present invention is capable of controlling when the material is applied to a sheet of metal so that the material will not be applied in the areas to be folded or the areas adjacent the leading and trailing edges of the sheet of metal. There also is no requirement that the specific areas to which the material is not to be applied has to be the same. Of course, as long as a single size refrigerator cabinet is being produced, it will be.
Furthermore, because the sheet of metal is moving at a rather rapid feed rate such as 350 feet per minute, the omission of the application of material to only four inches, for example, on each side of the notch in which the fold occurs is an area that relatively quickly passes the material applying means. Accordingly, the method and apparatus of the present invention must be capable of responding quickly and accurately to sensing signals which sense the presence of the notch in specific locations during its travel relative to the material applying means.